Wild Salmon Survival in the Balance – 1% may be the Crucial Tipping Point

Inland Fisheries Ireland (IFI) notes the recent Marine Institute (MI) publication which identifies that sea lice emanating from aquaculture facilities can cause mortality to wild Atlantic salmon. In this regard, the recent publication (Jackson et al, 2012) concurs with previously published international research (Krkosek et al, 2012 & Gargan et al, 2012). IFI welcomes the fact that there is now a clear acceptance of the negative impact of sea lice on juvenile salmon and the debate can now progress to identify the best methodologies to reduce or eliminate this impact. IFI would also like to see similar progress in relation to the issue of escaped farmed salmon.

In recent years approximately 5% of all juvenile salmon going to sea return back to their native rivers as adults to spawn. Precisely because natural mortality rates of salmon are high, even a proportionally small additional mortality from sea lice can amount to a large loss in salmon returning. To put this average 1% reduction in return rates, as reported by the MI, in context, if 3,000 salmon return to a river, and this represents a 5% return rate, a reduction in the return rate to 4% translates into a reduction of 1/5 (20%) of the adult salmon or 600 fewer fish returning. The Board of IFI is concerned that this level of additional mortality has the potential to curtail commercial or recreational salmon fisheries and impact on individual river salmon conservation limits and may be the tipping point between having an open or closed fishery.

The paper identified that just under 40% of released juvenile salmon showed a significant difference in return rate between sea lice ‘treated’ and ‘non-treated’ groups, indicating that mortality from sea lice is significant in 40% of the releases in the study. Unfortunately, there was a significant effect from sea lice in six different bays along the west coast over the study period.

This recent study provides further evidence that salmon will be impacted by sea lice. The location of salmon farms in relation to salmon rivers and the control of sea lice prior to and during juveniles salmon migration to their high seas feeding ground is critical if wild salmon stocks are not to be impacted. The development of resistance to chemical treatment of sea lice and other fish husbandry problems, such as pancreas disease and amoebic gill disease, are likely to make effective sea lice control even more difficult in future years.

Norway, one of the world’s biggest producers of farmed salmon are also seriously concerned about the impact of sea lice emanating from aquaculture facilities on wild salmon stocks and the issue of escaped farmed salmon. In their Strategy for an ‘Environmentally Sustainable Norwegian Aquaculture Industry’ produced by the Norwegian Ministry of Fisheries and Coastal Affairs they state:
“Even though salmon lice occurs in wild salmon and sea trout, it is an example of a parasitic disease which has been intensified by the multitude of hosts in aquaculture facilities. In addition to being passed from fish to fish, it can also be spread over long distances by currents”

They further state;
If delousing in fish farming fails to yield the desired effect on lice figures for wild fish, it may be necessary to consider a reduction in the biomass of the farming facilities (reduce the number of hosts) in the worst-affected areas.”

On the matter of escaped farm salmon, the Norwegian authorities have stated that “scientific comparisons of wild and farmed salmon, and their cross-breeds, has shown that gene transfer from farmed to wild salmon can reduce the latter’s ability to survive. This is why such gene transfer is one of the main problems with escapes”. IFI would like to see similar progress made on the issue of escaped farmed salmon as has been made on the sea lice issue.

IFI are supportive of the development of a sustainable aquaculture industry and welcome all advances in research that will underpin the sustainability of this industry and safeguard wild salmon and sea trout stocks into the future. Recommendations to address the issues of sea lice, escapes, location and scale have been made in IFIs submission to the Department of Agriculture, Food and the Marine on the Environmental Impact Statement regarding the Galway Bay fish farm development.